A proposed Denver ballot initiative that would reign in big-donor campaign contributions and set up a public financing system for city elections has been withdrawn by its backers.

“The Petitioners Committee has decided not to move forward with our ballot measure for November 2016,” said Elena Nunez, executive director of Colorado Common Cause, a backer of the initiative. “Given the well-funded opposition interests that have emerged, and the resources required for both the legal fight and a fall campaign amidst a crowded and expensive election season, we’ve decided to postpone our ballot measure.”

The 30 pages of revisions that backers proposed contained many changes, including a requirement for Denver to set aside up to $8 million every four years to match small-dollar contributions, lower contribution limits for the mayor and other elected officials and ban union and corporate contributions to candidates.

The measure was challenged by David Kenney, a political consultant and lobbyist who’s active in the business community, on June 27. The challenge alleges that the initiative is so wide-ranging that it violates a single-subject rule for ordinances and says the ballot title approved by the Denver Elections Division inadequately summarizes the measure and includes words intended to sway voters.

“We will continue to build the support needed to counter the powerful interests who are trying to maintain the status quo,” Nunez said. “We are committed to working together to advance these important reforms.”

Denver County Courts, in response to allegations by the Denver Auditor’s Office that it refusing to be audited, says it is “fully committed to financial transparency” and that it wants to meet with the office to discuss how to move forward.